Tutorial 1 Getting started
| Learning goals
| Prior knowledge |
As mentioned earlier these tutorials are focussing on providing the basic skills of knowledge engineering. In this first tutorial, the main dimensions of a ship will be systematically varied. The knowledge used is Archimedes’ Law in combination with design requirements, which are the following:
The ship should have
Our objective is to generate a dataset of systematically varied ships that meet the design criteria.
Before starting with your knowledge engineering, please make sure you are actually using the knowledge engineering user level and you have Quaestor configured in the most convenient layout.
To check/change your user level go to the general tab of Tools>Options. You can change your User level. If you are not able to change it to Knowledge Engineer (level 3), you do not have KE rights. Please contact your ICT department or Qnowledge for the proper license.
When Quaestor is started, you are presented with the opening screen, with no knowledge base or project loaded:
To create your first knowledge base
The screen changes to the main Quaestor knowledge engineering screen:
When a knowledgebase node is expanded, like Newqkb
here, the classes within the knowledgebase are visible. Classes are used to organise your parameters, and put them in a practicable structure. The Top Goals/Undefined class is part of the knowledge base by default. Here, the goal parameters of your calculation (Top Goals) can be stored, as well as other parameters that don't belong to other classes (Undefined).
Create a new class, named Main Dimensions, in which the following ship parameters are to be stored.
Lpp: Length between perpendiculars
B: Moulded breadth
T: Draught from keel to Construction Water Line
Main Dimensions
.Sub classes can be defined by right clicking on any class name and again selecting New Class.
The class is now shown in the knowledgebase tree, and you can add the parameters Lpp
, B
and T
.
Select the class Main Dimensions
and select Knowledge -> New parameter/function from the main menu. Alternatively, click in the right part of the knowledge browser, and select New Parameter / Function (Ctrl+I). Give the parameter the name Lpp
and click the Value button to select its type. Repeat these actions for the parameters B
and T
.
The added parameters now appear in the right part of the Knowledge browser like this:
A red cross draws your attention to the fact that a parameter is not yet fully defined for the system to use it.
The first requirement is already satisfied, so let's assign dimensions to the parameters.
?
into m
, the dimension for Lpp
(meters).You can also add a reference for a parameter. A proper reference is important, as users of the knowledgebase may not be certain of the exact meaning of the parameter. Please also read Documentation of knowledge for more details.
B
and T
, just as described above. Of course, the breadth and depth of the ship are defined in meters.Now only the last requirement for valid parameters has yet to be fulfilled: a way to be determined (input from the user or defined by a relation). This qualification can be provided in the Properties window.
Lpp
. In the Properties window, scroll down to the Determined by row. Change the value to VR: User only, as the parameter Lpp is input (instead of defined by a relation).
Notice that now, the status of the Lpp parameter has changed to
to show that Quaestor knows enough about this parameter to use it in a computational model. Now make sure that B and T are determined by VR: User only too. By the way, VR stands for Value Requested.
Note that above you have explicitly added Lpp
, B
and T
as parameters to the knowledge base. You are also able to implicitly add parameters by creating relations that contain new parameters. Quaestor will automatically add these new parameters to your knowledge base (so, implicitly). You will encounter this in the following section.
Tutorial 1
, by selecting File -> Save as.In order to define the loading capacity of the ship, it’s important to know the kind of water (Salt or Fresh) the ship will sail in. Therefore, you're going to add some relations and constraints, and make sure the user can select the watertype. Two relations must be added, one for salt water and one for fresh water.
Rho = 1025
(belonging to salt water), and click Save:
Note that when you enter a relation, Quaestor provides as much help as possible by means of the Help Checker. This checker shows what to expect (in this case a Value or an Expression, ValExp). After saving a relation, the Help Checker will check the syntax for possible errors, and shows a warning message when something is wrong.
Because of entering the relation, the parameter Rho
has automatically been created. For Rho
to be a valid parameter, a dimension should be assigned.
The parameter is automatically created in the Class in focus when saving the relation!
Rho
and assign it the dimension kg/m^3
. Rho
is now a valid parameter. Furthermore, make sure Rho
is determined by SYS: System/Equation, as a relation is used to determine Rho
.What follows now might seem a bit unconventional: a second relation is given for Rho. This is a nice example of how Quaestor works: in a calculation, Quaestor can find numerous calculation paths and automatically chooses the most appropiate one, based on constraints and available data.
Rho = 998
The two relations for the density of the water are only valid for their corresponding watertype. Therefore, a constraint is added to each relation. A constraint is simply a restriction for the validity of the relation.
Click Top Goals/Undefined in the Knowledge browser: all relations in that class are shown (this will work for any class). One can always edit a relation by selecting it and pressing F2 (or right click and select Edit). This is also a useful method to find out which relation you actually selected.
Rho = 1025
in the Knowledge browser and select Constraint -> Add New. In the upper part of the new window enter the following constraint:Watertype$ = "SW"
and click Save:
The constraint is now added, and a parameter named Watertype$
has been created. The $
at the end of the parameter name makes sure Quaestor recognizes it as a String value, and the dimension Str is automatically assigned (see also Quaestor syntax). We have to assign a Determined-by value to make it a valid parameter.
Watertype$
is determined by VR: User Only, as the user should provide the information concerning the water type.Repeat the process for the other relation.
Watertype$ = "FW"
to the relation Rho = 998
.
Note that the expression editor assists you with the presentation of existing parameters and intrinsic functions.
Both relations are now connected to the corresponding watertype by means of the value of Watertype$
.
Whenever Rho
is needed in the calculation process, Quaestor will note that the watertype is needed to determine the value of Rho
, and will ask the user for this value (because it is assigned to be User only).
When you select a parameter in the upper list, the relations of that particular parameter are visible:
Moreover, when you select a relation in the lower list, the constraints for this relationship are shown:
Because there are only two possible values for Watertype$
(SW or FW), it's easy to integrate a dropdown box.
Watertype$
in the Knowledge Browser, select the Parameter tab and in the Reference box enter the following lines:FW<EQ>Fresh Water
SW<EQ>Salt Water
The use of a dropdown box will be clear in a later stage of this tutorial, when calculations are made. Note that you can add the @EQEXPLAIN attribute in the Data box ('data slot') of the Watertype$
parameter (see Frame Viewer for data slot) in order to display only "Salt Water" and "Fresh Water" are shown in the dropbox (so without SW and FW).
On the basis of the earlier defined parameters and the block coefficient Cb
, the displacement of the ship can be calculated.
DISP = Cb * Lpp * B * T * Rho / 1000
which defines the displacement of the ship in tons.
Note that two new parameters are created: the block coefficient Cb
and the displacement DISP
. In order to keep the knowledgebase meaningful, it is necessary to provide references, dimensions and determined-by values for these parameters.
Cb
and DISP
. Cb
has no dimension (-), DISP
should be in tons (t). Just press OK if Quaestor warns that tons is no base dimension (kg), it is just to inform you. We covered this by dividing DISP
by 1000. The determined-by values should be VR: VR User Only for Cb
, and SYS: System/Equation for DISP
, as the block coefficient is input and the displacement is determined by a relation. Verify that all parameters now have a blue cross instead of a red one in front of them:Let's perform your first Quaestor calculation. A solution is always determined by one or more Top Goals. A top goal is a parameter (or object) that is your final calculation target, in this tutorial it's the displacement of the ship.
DISP
.Note that the cross in front of DISP
changed to , indicating that it's a top goal for the calculation.
Calculations and solutions are managed in the Workbase. Here, solutions can be created, redone (with different data), examined and deleted.
The calculation progress is started, and Quaestor first wants to collect all input data in the Workbase window:
Entering data is easy: just type a value for each selected parameter and press enter to switch to the next one.
B = 10 Cb = 0.55 Lpp = 60 T = 6 Watertype$ = SW (Salt Water)
Note that the input of Watertype$
consists of a dropdownbox, which we created above:
After providing the data you have to press the Next button to continue. The actual calculation is started now and because this is a very simple example, the final state is alost immediately shown:
The top goal (DISP
) is shown, together with all parameters that were used for the calculation. With these input values, the displacement of the ship is about 2030 tons.
So far, you created one solution, which is shown in the workbase:
As mentioned in the objective, you will create a dataset of systematically varied ships. You could of course perform several calculations with different input data by hand, but it's much easier to use the ability of Quaestor to create multiple case solutions. To keep the complexity of this example within reason, you will only vary the breadth and length of the vessel. Please note that due to some important conceptual reasons, the latest Quaestor release can only perform calculations on ranges of parameters when you already have created a solution.
B= 9(0.5)11 Lpp= 55(2)69
In this way, B
and Lpp
are defined by a range, given the start value, step size and end value. For example, Lpp
is defined from 55 to 69 meter, with steps of 2 meter.
Quaestor will ask if it should create a case matrix for Lpp
(figure 15), click Yes (an explanation will follow).
You will see that the single value input is still in the list and the multi case values are in the table part of the Workbase. Press the Next button to continue.
The new solution is now created. The fixed values are again shown in the right hand side of the workbase. The varying parameters (B and Lpp) and the corresponding solution for DISP are shown in the lower part. Each row is a different case, identified by a case number(#1, #2, etc.), see figure 16.
Figure 16 Multiple case solutions are shown in the workbase, each row is a different case
What does the Case matrix question mean? Note that the variations of B do not correspond to the variations of Lpp: there are 5 values for B and 8 values for Lpp. If we would have answered No to the Case matrix question, five variations of B would have been made, each one with the corresponding value of Lpp (the last 3 Lpp values would be omitted). In that way, there would be only five cases. As we answered Yes to the question, all possible combinations are considered, which results in 5*8=40 cases. You can easily notice the difference by creating a new solution with the same input values, but now answer no to the case matrix question.
NOTE: Ranges can be defined in multiple ways:
Our multiple case solution table is sorted by the breadth of the ship, as shown in figure 16. Suppose we'd like parameter Lpp the leading parameter in this table.
In the knowledge browser, select the parameter Lpp. In the Slots & Properties window, scroll down to the row Output to, and select HEADER (figure 17). Now, refresh the table of the multiple case solution by clicking another solution, and then again the multiple case solution. The table is now leaded by Lpp.
Figure 17 By selecting Output to HEADER, the parameter will 'lead' the multiple case solution table
A lot of cases in our solution don't meet the design criteria: a displacement between 2000 and 3000 ton. We could have fixed this by adding a constraint to DISP, but another way is to use a filter in the solution table.
Range as filter, fill in 2000 for Lower bound and 3000 for upper bound (figure 18). Click the Apply button.
In the workbase, select the last (multiple case) DISP solution, and click the or "Filter" button. The filter window shows. For DISP, select
Figure 18 With a filter, cases that do not fulfill the filter conditions can be made invisible
Now, only the cases for which 2000<DISP<3000 are shown in the table. Our objective has been completed: we build a dataset of systematically varied ships that meet the design criteria.
You can verify your results by comparing it to [Tutorial 1 Finished]